Using a paring knife, score each wedge of squash lengthwise down the middle of the flesh. Heat the butter and oil in an 11- to 12-inch straight-sided sauté pan over medium-high heat. Arrange the squash in the pan in a single layer and cook, flipping occasionally, until deep golden-brown on all cut sides, about 10 minutes.

Carefully pour the wine into the pan, then quickly scatter the brown sugar, rosemary, lemon juice, 1/2 tsp. salt, and 1/8 tsp. pepper over the squash. Cover the pan, reduce the heat to low, and simmer until the squash is almost tender, about 10 minutes more.

Uncover the pan and increase the heat to medium. Flip the squash and cook until the liquid is thick and the squash is tender, about 5 minutes more. Transfer the squash to a platter, season with salt and pepper to taste, drizzle any remaining liquid over the top, and serve.